Process of making projectiles



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JOHN L. COX, 0F PHILADELPHIA, PENNSYLVANIA.

PROCESS MING PROJECTILES orena.

No Drawing.

To all whom it may concern:

Be it known that 1, JOHN L. Cox, a citizen of the United States, residing at Philadelphia, county of Philadelphia, and State of Pennsylvania, have invented a new and useful Improvement in Processes of Making Projectiles, of which the following is a full, clear, and exact description.

In the manufacture of armor piercing shot and shell the necessity of combining in a projectile formed of a single block of metal a hard but not brittle head with a relatively soft and very tough body is well recognized, and projectiles having in degree such characteristics have hitherto been manufactured.

Known processes of manufacture still leave much to be desired'in obtaining and combining these desirable and apparently contradictory qualities; moreover, a considerable proportion of projectiles that have been subjected to recognized methods of heat treatment designed to produce the desired result fail when subjected to the rigorous ballistic tests which they must pass to be accepted.

It is the object of my invention to manufacture a projectile which will possess to a maximum degree the qualities above memtioned, and by a process which will minimize the likelihood of producing any defects or weaknesses which might endanger acceptance or, later, cause spontaneous rupture in storage.

By my process aprojectile is produced having a-point characterized by a high degree of hardness, progressively decreasing through the head toward its junction with the body, and a body sufficiently soft to permit machining yet so tough that it will not break upon impact; moreover, the process is i one wherein the dangerof cracking duringv treatment is minimized, and all danger of theshell cracking in storage after delivery is removed. I

In the heat-treatment of steel certain law are more or less well lmown, but there are many conceivable, ways'of applying them to heat treating processes, and there is always the danger that while some of these; laws. may be regarded others-might be overlooked orign'ored. Y

The laws thatl have more especially process arethe followingzw E ;1. On heating attheAc point the previously existing cell. boundaries of the steelborne in mind inpthe development of I my Specification of Letters Patent.

. BSS.

Patented m.- 211, 11922.

Application filed November 20, 1920. Serial No. 425,433.

begin to disappear as the solution oommences, but. are not entirely gone until the.

Ac,- point is reached.

2. At the Ac point a new cell structure begins to form and to grow larger as the temperature increases.

3. There is a cell size corresponding 7. The power of hardening once acquired by steel on heating is not lost, on slow cooling, until the Ar point is passed. Generally this temperature shows a visible color.

8. Sudden cooling from below the Ar point, or generally from black, theoretically will not produce hardening but the steel will be in the same soft. or annealed state that it would be had it been slowly cooled.

It is much less well known that on heating, sudden cooling from a point within a substantial, but limnted, range below the Ac point as experimentally determined, may produce a distinct degree of. hardening and notable loss of toughness; while sudden cooling from a temperature too'far below ,the Ac point to produce this effect will impart a degree oftoughness superior to that resulting from a slow cooling from the same or somewhat higher temperature.

It is also known to but'few that the and Ac points are not fixed points for any particular composition but vary with the degree. of grain-refinementhof the steel, being lower as the grain of the steel; is finer.

, although specifically difi'e'rent from the presess ofhardening projectiles,- which'process,

ent process,v has features of novelty which are also combined in the present process.

Said application hence contains certain 1 claims broadly covering. the present proc- In :the present appllcatlon I claim such features of the present processas are,

novel, but not disclosed in the process of said earlier application. Moreover, the process of the present application is more specifically adapted to the treatment of shells made from nickel chrome shell steel (although not limited thereto) and I have used the. term black instead of the Ar, point, for the reason that in steel of this character the Ar, point is frequently very diflicult of determination and is sometimes unaccountably low.

I shall not herein describe the process of melting the steel and casting the shell ingots.

After casting, the shell ingots are reheated and forged. I prefer to quench them fora few minutes to prevent grain growth, but for too short a time to produce cracking. Whether so quenched or not, they are then cooled slowly until at least black throughout.

The forgings are then reheated in a continuous furnace to about 225 F. above the Ac, temperature (generally the same as the Ac temperature in steels of this-character) in order preliminarily to refine the grain. They are then removed from the furnace and cooled in the air until black throughout. The forgings are again reheated, in a second continuous furnace, to a temperature of about 75 F. above the Ac, point, to complete the refinement of the grain, and are.

then, in a third continuous furnace, so slowliy cooled as to prevent any appreciable harening of the steel which would interfere with the preliminary machining of the shell.

After preliminary machining, the shells are reheated to considerably above the Ac, point and quencheduntil well below black throughout, then reheated to a less degree above the Ac,'point and quenched again until well below'black, then again reheated to below the Ac, point and quenched until well below black, followed by a slower cooling to avoid unnecessar risk of crackin If the composition of the projectile has been properly chosen and all steps of melting, forging, and the heat-treatment de-' scribed above properly applied, the projectile will be in the condition of maximum toughness throughout, and soft enough readily to allow machining to finish sizes, should that step not already have been applied. It

. is generally advisable not to finish the band score at this stage.

After further machining, the shells are ready for hardening and are heated considerab y above the Ac, point and'quenched to cold; then raised to a temperature below 400? F. to relieve stresses, and thereafter allowed to cool.

The body of the shell is then heated close to the Ac, point and allowed to cool and is then reheated to a-temperatureclose to but, so far below the Ac, point that no hardening can result, and then quenched to well below black, preferably for somewhat less than the entire length and heated to avoid cracking. The shell is then inverted and placed point downward in shallow water to cool.

The heating and cooling of the projectile during the hardening and drawing may be carried out by any appropriate means, such, for example, as described in my above mentioned application.

In the foregoing steps, the first two coolings from above the Ac, point may be made from the same temperature, but preferably the second cooling is made from a lower temperature.

The temperature from which the two preliminary quenches are made can be the same, but preferably the second quench is from a lower temperature than the first.

If two similar coolings or quenchings were to be made from the same temperature, then the duration of the heat preceding the second cooling should be much shorter than that of the heating preceding the first cooling, to derive the full benefit from the step. The effect of the above treatments is to impart to the head the maximum degree of hardness at the point, and adiminishing degree of hardness towards the rear withoutimpairin the fine-grained structure of the steel, while imparting to the body the maximum degree of toughness, and a sufiicient degree of softness to enable it to be readily machined if desired, as, for instance, for the attachment of the band.

While it-is true that the elevation of the temperature of the rear of the head in the final heating operation due to the conductivity of the metal modifies somewhat its hardness, the modification 'is' such that it would be desirable to take special means to obtain it; that is, the objectionable brittleness necessarily associated with extreme hardness is largely eliminated where maxi,- mum hardness is not necessary, but there is secured a maximum degree of hardness consistent with the reduction of brittleness to the desired extent. However, the amount of heat transmitted from the head to the point during the cooling of. the head must be restricted to prevent diminution'of the hardness of the point. As it is usually dangerous to quench the whole projectile after' the heating of the body, in that the rojectile is likely to crack, I refer, as descri ed above, to quench some w at less than all the body so heated and subsequentl to submerge the point in water, thereby ho ding down the temperature of the point.

I wish it to be understood that there is no clearline of demarcation between the hard and tough portions of the projectile; on the contrary, there is between thehard point and the tough body the major portion of the head, shading in hardness from the point toward the body, which is not as hard as the point nor as tough as the major portion of the body.

The exact temperature corresponding to the A0,, Ac and Ar, points will vary with the composition and physical structure of the steel and the last'with the degree of the latest heating and cannot be definitely stated; but these points are well known to metallurgists and practical steel workers and are more informative than the specification of exact temperatures. Instruments of a number of forms exist for their accurate determination. By the term black 'is meant below visible redness in the dark or a temperature of about 950 F.

Having now fully described my invention, what I claim and desire to protect by Letters Patent is:

1. The process of heat treating projectiles which comprises forging the projectile and suddenly cooling the forging to prevent grain rowth but stopping the sudden cooling be ore cracks are produced, then cooling slowly until black throughout, then reheating the projectile to about 225 F. above the Ac, point, then cooling in the air until black throughout, then reheating to about 75 F. above the Ac, point, then slowly cooling, then reheating to considerably above the Ac, point and quenching until well below black throughout, then reheating -to a less degree above the Ac, point and quenching until well below black throughout, then reheating to below the Ac, point, quenching until well below black throughout and then more slowly cooling, then reheating to considerably above the Ac, point and quenching to cold, then heating to a temperature be-.

low 400 F. to relieve stresses and allowing to cool, then heating the body close to the Ac, point and allowing to cool, then reheating the body portion just treated to a temperature close to but so far below the Ac, point that no hardening can result, then quenching to well below black, and then cooling the point .in water and the body in air.

2. The process of heat treating projectiles comprising refining the grain by reheating forged projectiles to about 225 F. above the Ac, point, then cooling in air until black throughout, then reheating to about 75 F. above the Ac, point,- then slowly cooling, then reheating to considerably above the Ac, point, then quenching until well below black throughout, then reheating to a less degree above the Ac, point, then quenching until well below black, then reheating to below the Ac, point, quenching until well below black and then more slowly cooling; then hardening by reheating to considerably above the Ac, point and quenching to cold;

then heating toa temperature below 400 F. to relieve stresses and allowing to cool; and then toughening by heating the body close to but sufliciently below the Ac, point to prevent hardening, then quenching to well below black, and then cooling the point in.

in a furnace, then reheating to considerably above the Ac, point, then quenching until well below black throughout, then reheating to a less degree above the Ac, point, then quenching until well below black, then reheating to below the Ac, point, quenching until well below black and then more slowly coolingz' then hardening by reheating to considerably above the Ac point and quenching to cold: then de-stressing by heating to a temperature below 400 F. and allowing to cool; and then further treating the projectile to toughen the body without materially softening the point.

4. The process of heat treating projectiles comprising refining the grain by reheating forged projectiles to about 225 F. above the Ac, point, then cooling in air until black throughout, then reheating to about F. above the Ac, point, then slowly cooling in a furnace, then reheating to considerably above the A0, point, then quenching until well below black throughout, then reheating to a less degree above the Ac, point, then quenching until well below black, then reheating to below the Ac, point, quenching until well below black and then more slowly cooling: and then subjecting the projectile to a hardening treatment.

5. The process of heat treatin projectiles which comprises cooling the orged projectile from a high temperature; then subjecting the projectile to a grain refining and softening treatment including heating'it to a temperature substantially above the Ac, point and cooling slowly; and then subjecting it to a further grain refining treatment including heating to substantially above the Ac, point and quenching, and then heating to a temperature below the Ac, point and again quenching.

6. The process of heat treating projectiles l treatment including reheating to' a temperature materially above the Ac, point, then cooling in air until black, then reheating to a temperature above the A0, point but below the temperature of the immediately preceding heat, and then cooling slowly in a furnace; and then subjecting the shell to a succession of heating and cooling treatments to further refine the grain.

7. The process of heat treating projectiles which comprises subjecting the projectile to heating and coolin to refine the grain, then hardening by heating to considerably above the Ac point and quenching to cold, then heating to below 400 F. to relieve stresses and allowing to cool, then heating a portion 10 of the projectile from the base forward to a temperature approximating the Ac point,

and then quenching.

In testimony of which invention, I have hereunto set my hand, at Philadelphia, Pa., 15

on this 19th day of November, 1920.

JOHN L. COX. 

